On Sun, Jun 3, 2018 at 9:08 AM, Theo de Raadt <dera...@openbsd.org> wrote:
> Philip Guenther <guent...@gmail.com> wrote:
> > On Sun, Jun 3, 2018 at 3:26 AM, Klemens Nanni <k...@openbsd.org> wrote:
> > > Snap from 31.05.2018 with
> > >
> > > OpenBSD 6.3-current (GENERIC.MP) #0: Sat Jun 2 16:21:22 CEST 2018
> > > k...@x250.my.domain:/usr/src/sys/arch/amd64/compile/GENERIC.MP
> > >
> > >
> > > acquiring duplicate lock of same type: "&mp->mnt_lock"
> > > 1st vfslock @ /usr/src/sys/kern/vfs_subr.c:191
> > > 2nd vfslock @ /usr/src/sys/kern/vfs_subr.c:191
> > > Starting stack trace...
> > > witness_checkorder(9,ffffffff81ab15c8,bf,ffff800000d00040,21) at
> > > witness_checkorder+0x63d
> > > _rw_enter(0,1,0,ffff800000d00000) at _rw_enter+0x56
> > > vfs_stall(1,ffff800000025400) at vfs_stall+0xab
> > >
> > [Also reported by bluhm@ and others]
> > Is vfs_stall() the only place that locks (busies) multiple mounts?
> Isn't that also how unmount works? I believe it locks the mount it will
> be discarding, and the filesystem it is mounted upon. It is serializing
> against other activities, such as a new mount or another umount occuring
> against the same dir.
Hmm, yes, dounmount() can busy multiple filesystems concurrently when doing
a forced unmount of a filesystem which has a filesystem below it, but in
the normal case of unmounting a leaf filesystem I don't see where it would
have multiple filesystems busy concurrently.
I see vfs_stall() doing 1 lock per filesystem. Why does this report
> say there are duplicates?
The warning is not that a single filesystem is being locked recursively by
a single thread, but just that a single thread is holding locks on multiple